Oil-cooled transformer



Dec. 30, 1958 J. B; WADHAM'S I 2,866,952

OIL-COOLED TRANSFORMER Original Filed April 6, 1951 2 Sheets-Sheet 1 Z g N14 1i g v I; i

INVENTOR. fines E MONA/"I5 1953 J. B. WADHAMS 2,866,952

OIL-COOLED TRANSFORMER Original Filed April 6, 1951 2 Sheets-Sheet 2 V IIVVENTOR. fifa/W55 5 Maw 5 United States Pater oIL-CooLED TRANSFORMER James B. Wadhams, Cleveland, Ohio, assignor to The Ohio Crankshaft Company, Cleveland, Ohio, a corporation of Ohio Original application April 6, 1951, Serial No. 219,615. Divided and this application November 1, 1956, Serial No. 623,514

1 Claim. (Cl. 336-58) it will be appreciated that the invention has broader ap-- plications. Such transformers normally include a primary windmg, a secondary winding and, if the transformer is to have high efficiency with relatively small sizes, a pow-- dared-iron core, all arranged in operative relationship. Powdered-iron cores have internal eddy-current losses which generate heat and this heat must be constantly removed during operation of the transformer. In order to effect this cooling, it is normally conventional to submerge the core in cooling oil which carries the heat away from the core to a point where it may be dissipated. Even so, dilficulty has been experienced in obtaining good heat transfer to the oil from the core. Also, the provision ofsuch a core with a minimum of internal losses and a good magnetic coupling with both the primary and secondary has been difiicult to obtain.

The cooling of the oil itself has also presented a problem. Heretofore, a cooling coil has been submerged in the oil through which water is continuously circulated. However, the magnetic field about the primary coil in transformers of this type is relatively large and, unless the cooling coil is removed a substantial distance from the primary coil, the tendency is for voltages to be induced in the cooling coil which appear across the inlet and outlet ports of the cooling coil or result in circulating current losses in the coil itself. This problem may be particularly emphasized when it is realized that in some transformers of the type to which this invention refers, there may be as much as three to five hundred volts per turn voltage gradient between each turn of the primary coil. If the cooling coil should have so much as the equivalent of one turn in coupled relationship with the primary coil, voltages of the same order as that appearing per turn across the primary coil will appear across the inlet and outlet ports for the cooling coil. This problem has heretofore placed a severe limitation on the construction of small, compact, efiicient, high-frequency, high-power transformers.

The present invention contemplates a transformer construction and cooling arrangement which is simple in construction, small in size, inexpensive and which overcomes all of the above referred to difficulties and others.

In accordance with the invention, a transformer is provided comprised of coaxial primary and secondary coils electrically insulated from each other by imperforate insulating means which extend beyond the ends of the coils to form a sealed, liquid-filled housing for the inner coil. A cooling coil, including cooling-fluid inlet and outlet ports is submerged in the liquid in the upper.

end of the housing spaced from but in unavoidable inductive relationship with'the primary coil, the cooling coil being so constructed and arranged as to have a minimum inductance as measured across the cooling-fluid inlet and outlet ports.

The high-voltage end of the primary coil is located remote from this cooling member such that the potential gradient in the oil between the high-voltage terminal and ground is a minimum. The invention also contemplates a magnetically-permeable core positioned inside the pri-.

mary coil formed of spaced axially-extending segments which may be readily assembled with the primary and which provide a maximum of liquid coolant passages therethrough, each segment generally having on its end an outward radially-extending portion overlapping the ends of the primary to improve the electrical coupling with the outer secondary coil.

Further, in accordance with the invention, the insulated housing between the'primary and secondary coil is so arranged as to provide a generally uniform voltage gradient between the secondary and primary as well as to facilitate assembly of the coils with the housing.

The principal object of the invention is the provision of a new and improved transformer construction which is easily manufactured, occupies a minimum space for a given power-handling capability and provides a maximum of electrical efficiency.

Another object of the invention is the provision of a new and improved cooling arrangement for oil-filled transformers which includes a cooling coil submerged in the oil and in the magnetic field of the coils of the transformer, the cooling coil being so arranged and constructed that its inlet and outlet ports may be electrically insulated and do not have voltages appearing thereacross.

Another object of the invention is the provision of a new and improved core construction for transformers of the type referred to which is easily assembled with the primary coil and provides a maximum of cooling passages therethrough for cooling oil, a maximum of electrical coupling with the secondary coil and has a minimum of electrical losses.

Another object of the invention is the provision of a new and improved transformer construction wherein the insulation between the primary and secondary is extended beyond the ends of these coils to form a sealed housing to hold cooling oil therefor.

Another object of the invention is the provision of a new and improved transformer construction employing a sealed oil-cooled housing wherein one of the coils is lo cated exteriorly of the housing and a minimum of electrical or cooling connectionsthrough the housing is re quired.

The invention will be specifically set forth and defined The invention may, of course,'

in the appended claims. take physical embodiment in a number-of equivalent but different-appearing forms and arrangement of parts, a

preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawing wherein:

Figure 1 is a side sectional view of a high-frequency, high-power transformer embodying the present invention;

Figure 2 is a sectional view of Figure 1 taken approximately on the line 22 thereof;

Figure 3 is a sectional view of Figure 1. taken approximately on the line 3-3 thereof;

Figure 4 is a top plan view of an alternative form of cooling coil; and

Figure 5 is a'sectional view of Figure 4 taken approximately on the line 5--5 thereof.

Referring now to the drawings where again it should be emphasized the showing is for the purposes of illustration only and not for the purposes of limitation, the figures show a multipiece housing A which is generally cylindrical in shape witha vertical axis, a multiturnprimary coil B in the lower part of the housing A, a single-turn secondary coil C coaxialwith the primary coil Band external of the housing A, a hollow powdered-iron core D internally of the primary coil and a cooling coil E in the upper part of the housing A.

, The housing A is comprised generally of an upper cylindrical part 10 telescoped overa lower cylindrical part 11, both formed of an electrical insulating material. The part. 11, as will appear,.has high potential'stresses thereinand is of .a high quality material such as polytetrafiuoroethylene. The'inner surface of the, upper part 10 is grooved and an O ring 13 in the groove bears agains the outer surface of the lower part 11 and provides afiuid-tight seal. The lower portion llopposite the ring 13 has a shallow counterbore in which a rigid ring member .of insulating material fits and prevents collapse of the part 11 under pressure of the O ring 13.

The lower end of the lower part 11 is closed by a cover member 17 which fits into a counterbore on the lower end of the part 11. An 0, ring 18 positioned in a groove 19 in the outer periphery of thecover 17 provides a fluid-tight .seal at this point. A clamp ring 20 surrounds the part 11 opposite the cover 17 and holds the part 11 against pressure of the 0 ring 18.

n The upper end of the upper part is closed in a similar fashion by a cover member 22 which fits into a counterbore on the inside of the. portion 10 and has an O ring 23 in a groove 24 on the outer periphery thereof tosprovide'a fluid-tight seal with the portion 10. Generally, the portion 19 may be made of an insulating material which does not need reinforcement opposite the O ring 23 as is necessary with the lower portion 11 which, being formed of polytetrafluoroethylene, tends to how slightly under continued pressure, thus necessitating the reinforcing rings and 2%.

A stud 12 formed of insulated material is threaded at its lower end into an opening in the lower cover 17 and extends coaxially of. the housing A and coil B through an opening in the upper cover 22 where a nut threaded on the upper end holds the covers 17 and 22 in tightassembled relationship with the respective parts of the housing A.

The housing A is filled with a cooling fluid 14, such as .transformer oil with a high dielectric strength, to the level as generally indicated by the numeral 15. An oil level gage 16 of conventional construction is supported on the outside of the upper part lit) by being threaded into an opening in the side of this upper part.

The primary coil B is comprised of a plurality of spaced insulated turns of a continuous length of rectangular copper tubing 25, the upper end 26 thereof extending vertically upward to a terminal member 27 of any suitable construction mounted in the upper cover plate. 22. The lower end of. the coil extends axially downwardly and connects with a terminal member 29 mounted in the lower coverv piatell'. .Obviously, these terminals could be positioned elsewhere if desired; but, in accordance with the invention, the lower terminal 29 forms a high-voltage terminal for the primary coil B and is positioned on the side of the primary coil B remote from the cooling coil E. As shown, the tubing has a continuous internal passage 3'') through which cooling water may be continuously circulated, the. terminals 27 and 29 being so constructed that cooling water may be circulated thereinto atthe same timethat theelectrical connections are made to the primary coil B. As shown, the portion of the tubing 25 forming the coil turns is wrapped with insulation 32 as is conventional.

The secondary coil :0 in the embodiment shown is a single-turn secondary, surrounds the part 11 opposite the genome coil B and is comprised of a generally C-shaped casting having closely spaced ends 34, 35 which are tapped or otherwise suitably formed to provide output terminals for the transformer. Hollow copper tubing 37 brazed to the outside of the secondary coil C provides water cooling therefor and removes any heat generated by the passage of high electric currents through the secondary coil. A threaded boss 38 on the back side of the coil C provides means for attaching the entire assembly to a support (not shown).

As shown, the inner surface of the coil C has a down ward and outward taper which corresponds with an upward and inward taper on the outer surface of the housing part 11. This construction facilitates ready assembly of the secondary C, onto the housing A and, at the same time, provides an increased spacing between the primary coil B and the secondary coil C from the lowvoltage end of th'e'coil Bto the high-voltage end. This construction-provides a more uniform or constant 'voltage gradient through thehousing A, as it will be appreoiated that thesecondary coil C generally operates at or near. ground potential, while the high-voltage end of the coil B may operate at radio-frequency potentials as high as'13,000 volts. -The' core D is generally in the form of a hollow cylind'er positioned internally of the primary coil B. This core is made up fro'ma plurality of segments U shaped in side plan" view having an elongated base 40 generally rectangular in cross-section and a pair of short legs 41 extending radially outwardly over the ends of the coil B but slightly spaced from the inner wall of the housing A. The inner surface of eachsegment has a pair of shallow, eircumferentially-extending grooves 42 into which a C-shap'ed snap ring 43 is positioned after the segments' are assembled in position on the interior of the 'coil B. Withth'e cross section of the base 40 as shown,*there*is providedbetween each segment of the core D, a wedge or pie-shaped axially-extending space 45 through which space oil or other cooling liquid in which the core D may be submerged may flow; and, in particular, as the cooling fluid heats, may flow upwardly by convection.

The cooling coil E is'positioned in the upper part of the housing A submerged below the level of the oil therein. The coil has a continuous internal passage therein through which a cooling medium such as water may be continuously circulated, the water being circulated intothe coil through an inlet fitting and out of the coil through an identical outlet fitting 51. In the embodiment shown, because of space restrictions, the coil E is located unavoidably within'the magnetic field of the primary coil B and is so constructed and arranged as to have a maximum of coolingsurface, such as may be provided by continuous lengths'of tubing, but with a minimum or, preferably, zero inductance so that the flux field of the primary coil B .will not generate voltages in the coil which will appear between the inlet fitting 5i) and the outlet fitting 51. Such voltages might be dangerous or, if copper pipes are used connecting to the inlet and outlet parts, would cause power-wasting currents to flow. In the embodiment shown, the cooling coil E is comprised generally ofthree aligned coils, an upper coil 54, an intermediate coil and a lower coil 56. The upper coil 54 is comprised of six short lengths of copper tubing, the ends of which are mitered and brazed together to substantially the configuration shown in Figure 3. This coil is comprised essentiaily of two turns wound in reverse. directions so that any voltages inducedare cancelled out. One end of the coil 54-connects tothe inlet port 5t). through a short vertically-extending length of copper tube 58. The other end of the coil 54 is con nected by a short length of downwardly-extendingcopper tubing 59 to one end of-the-intermediate coil 55. The intermediate coil, ina manner similar to'the'upper coil 54, is comprised of a plurality of short lengths of copper tubing, the ends of which are mitered and brazed together to the configuration substantially as shown in the figures. In this coil, it will be noted that the legs are relatively close spaced so as to minimize the inductance thereof and the configuration is such that there are two turns wound in opposite directions. The far end of the coil 55 connects to a short downwardly and vertically-extending tube 60 which connects to one end of the bottom coil 56, which coil is again made out of a plurality of pieces, in this case four short lengths of copper tubing, the ends of which are mitered to the configuration shown. This coil has a small diameter to hold its inductance to a minimum. The other end of this coil connects to the outlet port 51 through a vertical upwardly-extending short length of copper tubing 61.

It has been found that a coil having the configuration as shown in the drawings has a minimum of inductance and, therefore, has a minimum of voltage induced therein across the inlet and outlet fittings 50, 51 and, yet, the coil presents a maximum of cooling surface to the oil in the housing A.

In the preferred embodiment, the tubing employed is of the type having an externally-finned surface to increase the area of contact between the coil and the cooling oil.

In operation, cooling water is continuously flowed through the interior of the cooling coil E, through the interior of the primary coil B and through the tube 17 brazed to the interior surface of the secondary coil C. 'The transformer operates with the axis of the primary coil vertical and i filled with oil generally to the level as indicated by the line 15 which is over the upper surface of the upper cooling coil 54. In operation, the high-frequency flux field about the primary coil B created by high-frequency currents flowing therein flows internally of the coil B in the core D and thence around the outside of the coil where it threads into the secondary coil C, generating voltages in the secondary proportionate to the turns ratio of the two coils. The highfrequency currents in the core D tend to generate eddy currents Within the core which generate heat. This heat flows to the exterior surface of the segment by conduction in the core and is transferred to the cooling oil. As the cooling oil is heated, it tends to rise by convection in the passages 45 until it comes in contact with the cooling coil E where the heat is transferred to the coil and the cooled oil then flows downwardly through the interior of the core D to the bottom side and thence back upwardly through the spaces 45. It will thus be seen that there is a continuous movement of oil within the transformer to provide a maximum cooling effect on the core D. With the relatively narrow segments of the core D, it has been found that the tendency for eddy currents to be generated is considerably reduced which may in part be explained by the fact that there is a greatly reduced length of possible current path over a circumferentially continuous core member. The construction of the core D shown has proven extremely effective in practice and it is possible to operate the transformer and all portions thereof at temperatures far 6 below the critical temperature while handling extremely large amounts of power through the transformer.

Obviously, the transformer could be employed for step-up purposes wherein the secondary coil C could be a plurality of turns in excess of the number of turns of the primary, or the coil C could be used as a primary and the coil B used as a secondary.

Figures 4 and 5 show an alternative embodiment of a cooling coil also capable of accomplishing the object of the invention. In this alternative embodiment, a coil is provided in the shape of a conical spiral, the individual turns of the spiral being comprised of a pair of close-spaced parallel lengths of copper tubing 70, 71. The outer ends of these lengths of tubing terminate in an upwardly-extending portions 72, 73 which connect respectively to the inlet and outlet ports. The other ends of the tubes 70, 71 are interconnected as at 76 so that internal passages 74, 75 respectively are continuous from the inlet port to the outlet port. With the construction shown in Figures 4 and 5, a voltage potential may exist between the inlet ports 72, 73 and the other ends of the tubing at point 76, but this produces no difliculty because these points are electrically insulated. On the other hand, the cooling water flows through generally equal lengths of tubing and an equal number of turns, but with one half of the turns being wound in a direction opposite from the other half of the turns, so that any voltages which might be induced therein are cancelled out.

Obviously, other equivalent constructions and arrangements will occur to others upon a reading and understanding of this specification and it is my intention to include all such modifications and alterations insofar as they come within the scope of the appended claims or are the equivalent thereof.

Having thus described my invention, I cltum:

In a high-frequency transformer comprising a helical multiturn primary coil having a vertical axis, an insulating housing comprising an imperforate cylinder and liquid-tight means closing the end of said cylinder below the end of said primary coil and a cooling liquid filling said cylinder to above the level of said primary coil, a cooling coil submerged below the level of said cooling fluid and in inductive relationship with said primary coil, said cooling coil having inlet and outlet ports for a cooling fluid and a continuous path therebetween, said coil being comprised of a pair of turns each being wound in a direction opposite to the other whereby said coil is substantially noninductive and no voltage differential will exist between said inlet and outlet ports due to induced voltages in said coil.

References Cited in the file of this patent UNITED STATES PATENTS 853,843 Troy May 14, 1907 1,140,843 Nichols May 25, 1915 2,469,100 Andrus May 3, 1949 2,476,121 Smith July 12, 1949 2,577,825 Strickland Dec. 11, 1951 FOREIGN PATENTS 456,805 France Sept. 5, 1913 

